World number one Ashleigh Barty in action. File photo

World number one Ashleigh Barty pulled out of the US Open Thursday over "significant risks" from the coronavirus pandemic in a major blow for the Grand Slam, which is scheduled to start in New York on Aug. 31.

The Australian is the biggest name so far to withdraw from the tournament, with her decision coming as the United States marked a grim milestone when its COVID-19 deaths topped 150,000.

"My team and I have decided that we won't be travelling to the US for the Western and Southern Open and the US Open this year," she said in a statement to Australian media.

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"I love both events so it was a difficult decision but there are still significant risks involved due to COVID-19 and I don't feel comfortable putting my team and I in that position.

"I wish the USTA all the best for the tournaments and look forward to being back in the US next year," she added.

Her decision came despite the New York area keeping coronavirus cases at a relatively low level since spiking in March and April while areas such as Florida, Texas and California have become hotspots.

There have been more than 4.4 million detected infections in America so far.

It was not unexpected from Barty, who last month expressed concerns about the US Open going ahead, and she won plenty of support Thursday on social media for her "sensible" decision to give it a miss.

The 24-year-old, who surged to the top of the rankings last year and has stayed there since, said she would continue to monitor the situation before deciding whether to travel to Europe to prepare for a defence of her French Open crown.

"I will make my decision on the French Open and the surrounding WTA European tournaments in the coming weeks," she said, with Roland Garros due to start on September 27.